Double-pulse measurements of laser-induced alignment of molecules

The nonlinear interaction of molecules with intense laser fields is a poten tial method of preparing states with very high degrees of alignment. The ph ysical rotation of molecules can be confirmed using two pulses of orthogona l polarization and by observing the behaviour of the lowest fragmentation c hannels. New results show that this dynamic alignment is molecule specific. In the case of H-2, virtually all molecules are depleted by the pump pulse , but we see no evidence for rotation of I-2, in agreement with recent syst ematic studies of angular distributions. Further analysis indicates that th e ubiquity of laser-induced alignment has thus far been overestimated.